Variable displacement refrigerant compressors have been employed in engine driven automotive air conditioning systems in order to reduce engine load variations associated with compressor cycling. Such compressors typically cannot withstand sustained high speed operation without destroking to minimum displacement. As an engine driven accessory, however, the compressor speed is dependent on the engine speed, which can vary quite rapidly under various operating conditions.
In the past, high speed durability concerns have been addressed by declutching the compressor in response to the detection of potentially destructive compressor or engine speeds. Unfortunately, this requires the use of limits which are either specific to a particular installation or unduly conservative.